In order to meet the demand for protection of interior trim of automobiles against deterioration, which has been increasing with the recent trend to luxury of the interior trim, and to reduce the load of air conditioning, various glass having ultraviolet and infrared absorbing power has recently been proposed as window glass for automobiles. Among these proposed glass, for rear side window and rear window glass of automobiles, a glass having a low visible light transmission is preferentially used in view of protection of privacy. As such glass, mention may be made of the following glass.
For example, a colored glass composition for window glass disclosed in JP-A-6-503300 (PCT) is a glass having total energy transmission (T.sub.E) which is smaller than a light transmission under the illuminant A (TL.sub.A). Regarding a glass having a thickness of 3.85 mm, T.sub.E is 10 to 48% and TL.sub.A is 20 to 60%. This glass contains, in % by weight: 0.45 to 2.5% Fe.sub.2 O.sub.3 (total iron content), 0.001 to 0.02% CoO, 0 to 0.0025% Se and 0 to 0.1% Cr.sub.2 O.sub.3, as colorants.
A neutral dark gray glass disclosed in U.S. Pat. No. 5,393,593 claims in claim 25 a colorant comprising in soda-lime-silica glass, in % by weight: 1.00 to 2.2% Fe.sub.2 O.sub.3 (total iron), at least 0.20% FeO, 0.0005 to 0.005% Se and 0.010 to 0.030% CoO. This glass has a light transmission of 35% or less and a total solar infrared radiation transmission of less than 20% at a thickness of 3.9 mm.
A gray soda lime glass disclosed in JP-A-8-59287 (the term "JP-A" as used herein means an "unexamined published Japanese patent application) contains in soda-lime-silica glass a colorant comprising, in % by weight: 0.5 to 0.9% Fe.sub.2 O.sub.3, 0.012 to 0.025% CoO, 0.0025 to 0.010% Se and 0.005 to 0.020% Cr.sub.2 O.sub.3. The colorant is used in an amount which makes a glass have a light transmission (TL) of less than 30% and an excitation purity (P) of less than 12%.
Further, a dark gray glass disclosed in JP-A-8-157232 contains in soda-lime-silica glass a colorant comprising, in % by weight: 0.8 to 1.4% Fe.sub.2 O.sub.3 (total iron content), 0.21% or less FeO, 0.05 to 1.0% TiO.sub.2, 0.02 to 0.05% CoO, and 0.0005 to 0.015% Se.
The colored glass composition for window glass disclosed in the above-described JP-A-6-503300 (PCT) has a relatively high visible light transmission and, therefore, privacy protection effect attempted by the present invention cannot be achieved. Further, in order to obtain a desired tint, a large amount of Fe.sub.2 O.sub.3 is used.
The neutral dark gray glass disclosed in the above-described U.S. Pat. No. 5,393,593 has a high total iron content.
Further, the above-described any conventional glass does not essentially contain nickel but contains a high concentration of selenium, whereby desired optical characteristics can be obtained.
Selenium is vaporized in the course of melting in an amount of nearly 90% of batch charge. Therefore, it must be previously added to the batch in an amount of about ten times the required amount. Selenium is, however, extremely toxic, so that using such a large amount of selenium is not desirable from the standpoint of prevention of environmental pollution.
The above-described glass has a high total iron content. Therefore, due to radiant heat resulted from heat radiation absorbing effect of ferrous oxide, temperature at a crown of a melting tank may have the possiblity to reach its heat-resistant temperature or more in the course of melting. Thus, the production of glass by means of an ordinary glass melting tank has many difficulties.
The gray soda lime glass disclosed in the above-described JP-A-8-59287 uses a large amount of Se and Cr.sub.2 O.sub.3 in order to obtain a desired tint.
As can be seen that Cr.sub.2 O.sub.3 is often observed as black particles of chromite stone in glass, it is difficult for Cr.sub.2 O.sub.3 to melt in glass, and high temperature is needed to melt. Therefore, use of Cr.sub.2 O.sub.3 is not preferable in a practical production.
The dark gray glass disclosed in the above-described JP-A-8-157232 also uses a large amount of Se in order to obtain a desired tint. Further, total iron content is relatively high. Therefore, the content of TiO.sub.2, i.e., a colorant for cutting ultraviolet radiation, is small.